The present invention relates to a device and method for determining the occurrence of an intermittent short circuit. More particularly, the present invention relates to an intermittent short circuit determining device and an intermittent short circuit determining method that detects overcurrent flowing through an electric circuit of an automobile.
U.S. Pat. No. 4,023,264 describes a blade fuse installed in a fuse box of an automobile. Blade fuses, which are often used in electric circuits of automobiles, have a slow-burn characteristic. Due to the slow-burn characteristic, blade fuses are not melted by momentary excess currents but are melted by continuous excess currents that flow for a certain period of time.
Blade fuses normally melt and break when a dead short circuit occurs but do not break when an intermittent short circuit occurs. A dead short circuit causes a large amount of current to continuously flow in an electric circuit. An intermittent short circuit causes current to flow intermittently and within a short period of time in an electric circuit. An intermittent short circuit is a short circuit, which occurs when, for example, vibrations cause the electric wiring of an automobile to contact the body of the automobile. When an intermittent short circuit current continuously flows through the electric circuit of the automobile, for example, the electric circuit may be over-supplied with current. Thus, there is a need for an intermittent short circuit determining device that accurately detects the occurrence of an intermittent short circuit.
One of the inventors of the present invention disclosed intermittent short circuit determining devices in Japanese Unexamined Patent Publication Nos. 11-273544 (Japanese Patent Application No. 10-90866) and 2000-90808 (Japanese Patent Application No. 10-255204). The disclosed intermittent short circuit determining devices accurately detect the occurrence of intermittent short circuits. However, the prior art intermittent short circuit determining devices include separate parts for determining the occurrence of an intermittent short circuit and for disconnecting the electric circuit. This makes the prior art intermittent short circuit determining devices large and expensive.